1. Field of the Invention
The present invention relates to a method of configuring any given n-th degree filter, and more particular to a method of configuring an n-th degree filter preferably applied to a switched-capacitor filter.
2. Description of the Prior Art
Conventionally, LC filters composed of coils and capacitors are well known as filter circuits. However, since these LC filters are large in size and high in cost, recently configuring filters by use of integrated circuits has been studied.
As methods of configuring such IC filters as described above, gyrators, active filters, digital filters, switched-capacitor filters, and so forth, have been considered. In particular, however, the switched-capacitor filters have been highlighted owing to various advantages such as a high possibility of realizing the filters by monolithic IC's using MOS transistors, excellent electric characteristics, wide applicable fields, low cost, and so forth.
However, thus far only leapfrog type and bi-quad type have been known as methods of configuring the switched-capacitor filters, and no method of configuring a filter which can realize any given n-th degree transfer function has been known.
In particular, in the case where a filter for a video signal band is required to be configured, a switching speed as high as 40 times higher than the reproduction band is required for the leapfrog type switched-capacitor filter. Further, in the case of the bi-quad type switched-capacitor filter, the method of determining the coefficients has not yet been well known, so that a deviation in coefficients is readily produced, thus causing problems in that the filter is unstable or it is impossible to realize the filter.